1. Field of the Invention
The present invention relates to a mold thickness adjustment mechanism for an injection molding machine comprising a toggle type mold clamping system.
2. Description of the Prior Art
In a toggle type mold clamping system of an injection molding machine, a fixed platen and a rear platen are connected by a plurality of tie bars, and a movable platen which is provided slidably with respect of the tie bars is driven by the toggle mechanism to clamp together a fixed die attached to the fixed platen and a movable die attached to the movable platen.
The toggle type mold clamping system is disposed between the rear platen and the movable platen, and the movement range of the movable platen which is driven by the toggle type mold clamping system is limited. The clamp completion position of the dies which are respectively attached to the fixed platen and movable platen is normally set as a locked-up state in which a toggle link of the toggle type mold clamping system is fully extended, and at this time the tie bars are extended by the toggle type mold clamping system such that a reaction force generated thereby serves as a mold clamping force. In order to obtain a set mold clamping force in a state where the toggle link is fully extended, the distance between the fixed platen and the rear platen must be adjusted by adjusting the position of the rear platen with respect of the fixed platen by means of the thickness of the dies in use and the set mold clamping force.
The distance between the fixed platen and rear platen is adjusted conventionally using a mold thickness adjusting motor to cause the rear platen to move toward the tie bars or away from the tie bars.
In applications to an injection molding machine, however, the dies may not be exchanged, and even if the dies are exchanged the mold thickness may not be modified and the mold clamping force may not be altered. Although an injection molding machine may almost never use a mold thickness adjustment mechanism, the machine is provided with a complex electrically driven mold thickness adjustment mechanism, thus making the injection molding machine itself an expensive item.
Hence the removal of the electrically driven mold thickness adjustment mechanism itself from an injection molding machine which is used when the dies are not exchanged or the mold thickness is not modified even if the dies are exchanged has been considered.
FIG. 2 is a schematic diagram of a mold clamping system not provided with a mold thickness adjustment mechanism. In FIG. 2, a rear platen 1 and a fixed platen 2 are connected by a plurality of tie bars 4. A movable platen 3 is slidably disposed on these tie bars 4. A toggle type mold clamping system is disposed between the rear platen 1 and movable platen 3, but is omitted from FIG. 2.
The distance between the rear platen 1 and fixed platen 2 is fixed, and the movable platen 3 is advanced (moved toward the fixed platen 2) by driving the toggle type mold clamping system which is provided between the rear platen 1 and movable platen 3 such that the movable platen 3 reaches a maximum position of advancement in a locked-up state where a toggle link is fully extended. Since the distance between the rear platen 1 and fixed platen 2 is fixed, the distance between the movable platen 3 and fixed platen 2 at this time is also fixed. In this locked-up state, a fixed side die 5a attached to the fixed platen 2 and a movable side die 5b attached to the movable platen 3 are clamped together such that a set mold clamping force is generated.
Even when a predetermined mold clamping force is obtained by fixing the mold thickness and locking up the toggle link of the toggle type mold clamping system such that the tie bars are extended by a predetermined amount, it may be necessary to modify the mold clamping force in accordance with the projected area of the molded product. In such a case, a spacer 6 of a predetermined thickness, for example, is used as shown in FIG. 2 such that the movable side die 5b is attached to the movable platen 3 via the spacer 6 to substantially alter the mold thickness. By adjusting the mold thickness, the set mold clamping force is obtained. Note that FIG. 2 illustrates a state in which the toggle link of the toggle type mold clamping system is fully extended such that the die 5 (the fixed die 5a and movable die 5b) are clamped together in a locked-up state.
By interposing the spacer 6 between the movable platen 3 and the movable side die 5b as shown in FIG. 2, the distance by which the mold thickness can be adjusted is equal to the thickness of the spacer 6. In order to obtain various different mold clamping forces while using a die having the same mold thickness, a plurality of spacers 6 having different thicknesses must be prepared and used appropriately. Alternatively, a plurality of spacers having a thickness of approximately several millimeters may be prepared and used stacked together to obtain a spacer of a predetermined thickness.
However, it is laborious to prepare a plurality of spacers having different thicknesses, and when a plurality of spacers are used stacked together, the margin of error accumulates such that an accurate mold clamping force cannot be obtained.